Semiconductor device

ABSTRACT

A semiconductor device according to the present invention comprises a first semiconductor integrated circuit  11  having a predetermined function, the first semiconductor integrated circuit outputting a required output signal, a second semiconductor integrated circuit  12  in which a plurality of MOS elements (PMOS transistor or NMOS transistor) for independently switching to and from a conducted state and a non-conducted state in accordance with a plurality of gate signals each having a different timing is provided and the plurality of MOS elements is connected in parallel to an output or an input of the first semiconductor integrated circuit, and a pulse generating circuit  13  for generating and outputting the plurality of gate signals φi (i=1, 2, 3) each having a different timing with respect to the plurality of MOS elements in the second semiconductor integrated circuit.

FIELD OF THE INVENTION

The present invention relates to a semiconductor device comprising atleast two semiconductor integrated circuits having different functions,more particularly to a technology for improving reliability andextending a life. A semiconductor device according to the presentinvention, when applied to an I/O pad, is very effective as asemiconductor chip for performing a wired data communication withoutside, and the semiconductor chip can be extensively used in a chipset. Further, according to the present invention, a semiconductor devicein which a substrate control circuit and a dynamic circuit are installedcan assure a remarkably long-life reliability.

DESCRIPTION OF THE INVENTION

In a semiconductor integrated circuit, an MOS element (MOS transistor),which is constantly left in a conducted state, can be used as a pull-upresistance. The pull-up means that a potential is stably maintainedthrough connection to the positive side of a power supply via aresistance, and the connected resistance is called the pull-upresistance. The pull-up resistance is often used in an I/O pad circuitfor performing a data communication between a semiconductor device andoutside, a keeper circuit in a dynamic circuit and the like.

In recent years, a technology for controlling a substrate potential ofan MOS transistor to be optimum was proposed in order to optimize avariability generated in delays due to factors such as a process, reducepower consumption and achieve a high-rate operation. In applying thetechnology, it is necessary to supply the substrate potential inaccordance with a characteristic of the MOS transistor such as thevariability due to a variability generated in the process. As a proposedmethod for realizing such, the semiconductor device is divided into aplurality of regions and an ON resistance value of the MOS transistorfor monitoring in each region is evaluated so that the generatedsubstrate potential is supplied to the MOS transistor in thecorresponding region based on a result of the evaluation, wherein a gatevoltage of the MOS transistor for monitoring is fixed to an ON-voltageside.

When the MOS transistor is constantly conducted to be used as thepull-up resistance, a large DC current is consequently generated at alltimes, which results in deterioration of the characteristic of the MOStransistor. The deterioration is generated in the same manner when theMOS transistor is constantly conducted as a monitoring device forgenerating the substrate potential.

As a known example of the characteristic deterioration, a saturationcurrent of the MOS transistor is significantly deteriorated due toage-related changes as a result of fixing the gate voltage to theON-voltage side. More specifically, when a temperature in a chip isincreased in a state in which the substrate potential is in a back-biasstate relative to the gate, an absolute value of a threshold voltage ofthe transistor increases through stages. As a result, the transistor isslowed down over time. To be specific, the MOS transistor maydeteriorate by approximately 20% due to a characteristic of thesaturation current, which possibly leads to the malfunction of thesemiconductor integrated circuit after an extended period of time. Sucha phenomenon is called NBTI (Negative Bias Temperature Instability).Recently, it was found out that the NBTI is caused by the leak of boronand the like (see “A Predictive Reliability Model for PMOS BiasTemperature Degradation Mahapatra”, S. S.†† Alam, M.A.\\ ElectronDevices Meeting, 2002. IEDM '02. Digest. International PublicationDate:†2002 On page(s): 505-508).

SUMMARY OF THE INVENTION

Therefore, the present invention has been implemented to solve theissues of the age-related deterioration due to the NBTI, and a mainobject of the present invention is to provide a semiconductor devicewhose characteristic is not deteriorated though it is used for a longperiod of time.

A semiconductor device according to the present invention comprises afirst semiconductor integrated circuit having a predetermined function,the first semiconductor integrated circuit outputting a required outputsignal, and a second semiconductor integrated circuit in which aplurality of MOS elements (PMOS transistor or NMOS transistor) forindependently switching to and from a conducted state and anon-conducted state in accordance with a plurality of gate signals eachhaving a different timing is provided and the plurality of MOS elementsis connected in parallel to an output or an input of the firstsemiconductor integrated circuit.

As an alternative constitution, the semiconductor device may furthercomprise a pulse generating circuit for generating and outputting theplurality of gate signals each having a different timing with respect tothe plurality of MOS elements in the second semiconductor integratedcircuit.

A pull-up resistance and current monitoring device used for generatingthe substrate potential, which were conventionally realized by havingone MOS element continuously conducted at all times, are realized byhaving the plurality of MOS elements connected in parallel anddispersively operating them in a time-shifting manner. Morespecifically, the second semiconductor integrated circuit comprises theplurality of MOS elements, and the plurality of MOS elements connectedin parallel is connected to the output or the input of the firstsemiconductor integrated circuit. When the gate signals are applied tothe plurality of MOS elements from the pulse generating circuit or thelike, the plurality of MOS elements is separately ON/OFF controlled, andthe gate signals are respectively applied to the plurality of MOSelements connected in parallel at the different timings. Thereby, theoutput signal of the first semiconductor integrated circuit isstabilized without being affected by which of the plurality of MOSelements is in the conducted state at a certain moment. The plurality ofMOS elements is dispersively operated in the time-shifting manner sothat the NBTI phenomenon in each MOS element due to the lengthy use isalleviated. As a result, a circuit configuration not easily affected bythe age-related deterioration can be realized. The circuits to be addedin order to prevent the age-related deterioration only demand a smallnumber of MOS elements. Then, the same functions (pull-up resistance,current monitor and the like) can be realized without largely changingthe conventional circuit configuration.

In the semiconductor device constituted as above is preferably developedwhen the first semiconductor integrated circuit is a substrate potentialgenerating circuit and the second semiconductor integrated circuit is acharacteristic monitor circuit. Drains of the plurality of MOS elementsin the second semiconductor integrated circuit (characteristic monitorcircuit) are connected in parallel to the input of the firstsemiconductor integrated circuit (substrate potential generatingcircuit) via respective sample hold circuits. Then, the output of thefirst semiconductor integrated circuit (substrate potential generatingcircuit) is connected to respective substrates of the plurality of MOSelements in the second semiconductor integrated circuit (characteristicmonitor circuit).

Operation states of the plurality of MOS elements, which arecharacteristic monitoring devices in a plurality of regions into whichthe semiconductor device is divided, are monitored and a result of themonitoring is fed back to the substrate potential generating circuit sothat the substrate potential in accordance with the operation state ofeach MOS element is generated and outputted. In the foregoing case, afeedback control is affected by the age-related deterioration resultingfrom the NBTI phenomenon in the MOS element due to the lengthy use. Inorder to deal with the problem, the plurality of MOS elements isconnected to the input of the substrate potential generating circuit viathe respective sample hold circuits so that the sampling and hold aretime-shifted relative to each other. Then, evaluations of the monitoringusing the respective MOS elements can be averaged. As a result, thesubstrate output of the substrate potential generating circuit is noteasily affected by the NBTI phenomenon and accordingly stays at asubstantially constant value in accordance with the characteristic ofthe MOS element.

The foregoing semiconductor integrated circuit is preferably developedas follows in the case in which an I/O pad circuit constitutes the firstsemiconductor integrated circuit. In the case in which the firstsemiconductor integrated circuit is a tristate buffer, a pull-up circuitconstitutes the second semiconductor integrated circuit. In the case inwhich the first semiconductor integrated circuit is a dynamic circuit, akeeper circuit constitutes the second semiconductor integrated circuit.In the keeper circuit, the gate signals for the plurality of MOSelements in the second semiconductor integrated circuit are suppliedfrom an NAND circuit whose two inputs are the output signal of the firstsemiconductor integrated circuit and a timing signal.

In the case in which the pull-up circuit with respect to the output ofthe tristate buffer comprises the plurality of MOS elements operatingindependently relative to one another, the output of the tristate buffercan be in such a stable state as not easily affected by the NBTIphenomenon due to the lengthy use. In the case in which the keepercircuit with respect to the output of the dynamic circuit comprises theplurality of MOS elements independently relative to one another, theoutput of the dynamic circuit can be in such a stable state as noteasily affected by the NBTI phenomenon due to the lengthy use.

In the foregoing semiconductor device, the plurality of gate signalspreferably has an identical frequency and different phases, and a summedvoltage of the gate signals is preferably substantially constant perunit time. Alternatively, the plurality of gate signals preferably hasan equal transition probability.

When the summed voltage of the plurality of gate signals issubstantially constant per unit time, a pull-up operation can bestabilized though the plurality of MOS elements independently operate atthe different timings. Further, when the plurality of gate signals hasthe equal transition probability, such a pull-up resistance that theplurality of MOS elements is constantly conducted as if they were oneMOS element is realized.

Further, a semiconductor device according to the present inventioncomprises a plurality of MOS elements and a logic circuit for generatinga plurality of gate signals inputted to gates of the plurality of MOSelements based on a input signal, the semiconductor device outputting arequired output signal, wherein the plurality of MOS elements isequivalent to the output of the required output signal of thesemiconductor device, and a value of the required output signal isdetermined irrespective of values of the other gate signals when any oneof the plurality of gate signals is a first logic value.

Further, a semiconductor device according to the present inventioncomprises a plurality of MOS elements and a plurality of switchelements, wherein the plurality of MOS elements is serially connected,gates of the plurality of MOS elements are commonly connected,substrates of the plurality of MOS elements are commonly connected, anend drain and an end source of the plurality of MOS elements areconnected to one sides of the respective switch elements, other sides ofthe respective switch elements are connected to a semiconductorintegrated circuit having a predetermined function, and the connectionsof the end drain and the end source are switched over in accordance witha control signal for controlling the switch elements.

Further, a semiconductor device according to the present inventioncomprises a plurality of MOS elements and a plurality of switchelements, wherein the plurality of MOS elements is connected inparallel, gates of the plurality of MOS elements are commonly connected,substrates and sources or drains of the plurality of MOS elements areconnected to one sides of the respective switch elements, other sides ofthe respective switch elements are connected to a semiconductorintegrated circuit having a predetermined function, and the connectionsof the substrates and drains or sources are switched over in accordancewith a control signal for controlling the switch elements.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated be way of example and notlimitation in the figures of the accompanying drawings, in which likereferences indicate similar elements and in which:

FIG. 1 is a block diagram illustrating a basic constitution of asemiconductor device according to a preferred embodiment of the presentinvention;

FIG. 2 is a circuit diagram illustrating a constitution of acharacteristic monitor circuit according to a first preferred embodimentof the present invention;

FIG. 3 is a circuit diagram illustrating a constitution of a sample holdcircuit according to the first preferred embodiment;

FIG. 4 is a circuit diagram illustrating a constitution of a substratepotential generating circuit according to the first preferredembodiment;

FIG. 5 shows waveforms of timing signals of a pulse generating circuitaccording to the first preferred embodiment;

FIG. 6 shows circuit diagrams illustrating constitutions of a tristatebuffer and a pull-up circuit according to a second preferred embodimentof the present invention;

FIG. 7 is a circuit diagram illustrating a constitution of a pulsegenerating circuit according to the second preferred embodiment;

FIG. 8 shows waveforms of timing signals of the pulse generating circuitaccording to the second preferred embodiment;

FIG. 9 shows circuit diagrams illustrating constitutions of a dynamiccircuit and a keeper circuit according to a third preferred embodimentof the present invention;

FIG. 10 is an equivalence logic diagram according to a fourth preferredembodiment of the present invention;

FIG. 11 shows circuit diagrams illustrating a constitution of atwo-input NAND circuit and an enable signal generation logic accordingto the fourth preferred embodiment;

FIG. 12 is a truth value chart according to the fourth preferredembodiment;

FIG. 13 is a circuit diagram illustrating an example of application to aclock tree according to the fourth preferred embodiment;

FIG. 14 shows a monitor circuit according to a fifth preferredembodiment of the present invention; and

FIG. 15 shows a monitor circuit according to a sixth preferredembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, preferred embodiments of the present invention aredescribed referring to the drawings.

An example of a basic constitution according to a preferred embodimentof the present invention is described referring to FIG. 1. FIG. 1 showsa schematic constitution of a semiconductor device 10 commonly employedin first through third embodiments of the present invention describedlater. The schematic constitution is merely an example and may bemodified within the scope of an intended purpose of the presentinvention.

The semiconductor device 10 comprises a first semiconductor integratedcircuit 11, a second semiconductor integrated circuit 12 and a pulsegenerating circuit 13. An output of the pulse generating circuit 13 isconnected to an input of the second semiconductor integrated circuit 12.The first semiconductor integrated circuit 11 and the secondsemiconductor integrated circuit 12 are bi-directionally connected.However, the first semiconductor integrated circuit 11 and the secondsemiconductor integrated circuit 12 may be uni-directionally connected,wherein which of the first semiconductor integrated circuit 11 and thesecond semiconductor integrated circuit 12 serves as a receiving end isdifferent in the respective preferred embodiments. The firstsemiconductor integrated circuit 11 has an output port for outputting asignal to another semiconductor integrated circuit not shown.

First Preferred Embodiment

Referring to FIGS. 1 through 5, a semiconductor device according to thefirst preferred embodiment of the present invention is described.

The first preferred embodiment relates to an example of a semiconductordevice for supplying an optimum substrate potential to an MOS transistorin the another semiconductor integrated circuit. In the presentembodiment, the second semiconductor integrated circuit 12 is acharacteristic monitor circuit (current monitor circuit) for monitoringa characteristic of each region of the semiconductor device 10. Thefirst semiconductor integrated circuit 11 is a substrate potentialgenerating circuit for generating a substrate potential in accordancewith the characteristic of the MOS transistor monitored by thecharacteristic monitor circuit.

FIG. 2 is a circuit diagram illustrating a constitution of acharacteristic monitor circuit 12 a.

The characteristic monitor circuit 12 a comprises n number of MOStransistors of an N-channel type QN1, QN2, . . . , QNn each having anidentical shape and size. Drains of the NMOS transistors QN1, QN2, . . ., QNn are connected to equivalent constant power supplies 21. Sourcesand substrates of the NMOS transistors QN1, QN2, . . . , QNn arecommonly connected, while gates thereof are connected to a pulse outputterminal of a pulse generating circuit 13 so as to input a timing signalφi (i=1, 2, . . . , n). The drains of the NMOS transistors QN1, QN2, QNnare connected to an input terminal of a substrate potential generatingcircuit 11 a shown in FIG. 4 via sample hold circuits 14 a shown in FIG.3. The commonly-connected substrates of the NMOS transistors QN1, QN2, .. . , QNn are connected to a substrate output port BN of the substratepotential generating circuit 11 a.

The n number of NMOS transistors QN1, QN2, . . . , QNn correspond to aconventional single NMOS transistor constantly conducted and functionsin the same manner.

The NMOS transistors QN1, QN2, . . . , QNn are independently switched toand from a conducted state and a non-conducted state in accordance withthe timing signal φi (i=1,2, . . . , n) applied to the gates thereoffrom the pulse generating circuit 13. The NMOS transistors QN1, QN2, . .. , QNn further monitor voltage drops (resistance) thereof relative to aconstant current supply from a constant current supply 21 and supply aresult of the monitoring to the substrate potential generating circuit 1a via the sample hold circuits 14 a.

The pulse generating circuit 13 comprises n number of pulse outputterminals. From the respective pulse output terminals, the timing signalφi (i=1,2, . . . , n) as shown in FIG. 5 is supplied to the gates of theNMOS transistors QN1, QN2, . . . , QNn in the characteristic monitorcircuit 12 a. Because the n number of timing signals φi (i=1,2, . . . ,n) are shifted time-wise to one another, the NMOS transistors QN1, QN2,QNn are activated in a time-shifting manner without any duplication.

Outputs of the NMOS transistors QN1, QN2, . . . , QNn are respectivelyconnected to the corresponding sample hold circuits 14 a in order tostabilize respective inputs to the substrate potential generatingcircuit 11 a. The n number of sample hold circuits 11 a collectivelyconstitute a connecting circuit 14. The connecting circuit 14 is aspecific component in the present embodiment and not shown in FIG. 1.

FIG. 3 is a circuit diagram illustrating a constitution of the samplehold circuit 14 a. The sample hold circuit 14 a is provided so as tocorrespond to the NMOS transistor QNi (i=1, 2, . . . , n) and comprisesa sample capacitor C1, a hold capacitor C2, a comparator 22 and switchelements S1, S2 and S3. The corresponding NMOS transistor QNi isconducted by the timing signal φi (i=1, 2, . . . , n) transmitted fromthe pulse generating circuit 13. In the same manner, the switch elementS1 is turned on conducted by the timing signal φi, and the switchelements S2 and S3 are turned on by an inversion timing signal/φithereof. The switch element S1 and the switch elements S2 and S3 arereversely operated.

When the corresponding NMOS transistor QNi is in the conducted state inresponse to the timing signal φi, the switch element S1 is turned on,while the switch elements S2 and S3 are turned off. The monitoringresult from the NMOS transistor QNi is stored in the sample capacitor C1via the switch element Si. When the information of the sample capacitorC1 transmits through the comparator 22 to be thereby offset-processed,the monitoring result is evaluated. Next, when the timing signal φi isinverted to an “L” level, the NMOS transistor QN1 is non-conducted, andthe switch element S1 is turned off, while the switch elements S2 and S3are turned on. The monitoring result outputted from the comparator 22 isheld in the hold capacitor C2 and also transmitted to the input terminalof the substrate potential generating circuit 11 a via the switchelement S3.

FIG. 4 is a circuit diagram illustrating a constitution of the substratepotential generating circuit 11 a as the first semiconductor integratedcircuit 11. An output terminal of the connecting circuit 14 is connectedto the input terminal of the substrate potential generating circuit 11a. The connecting circuit 14 comprises the n number of sample holdcircuits 14 a respectively corresponding to the n number of NMOStransistors QN1, QN2, . . . , QNn. Output terminals of the sample holdcircuits 14 a are commonly connected and connected to the input terminalof the substrate potential generating circuit 11 a.

While the first NMOS transistor QN1 is being evaluated, an averageoutput value of the sample hold circuits 14 a corresponding to theremaining (n-1) number of NMOS transistors QN2 through QNn is outputtedfrom the connecting circuit 14. In the same manner, while the secondNMOS transistor QN2 is being evaluated, an average output value of thesample hold circuits 14 a corresponding to the remaining (n-1) number ofNMOS transistors QN1 and QN3 through QNn is outputted from theconnecting circuit 14. When any of the NMOS transistors is not subjectedto the evaluation, an average output value of all of the sample holdcircuits 14 a is outputted.

The substrate potential generating circuit 1 a comprises a differentialcircuit 31 and an output buffer circuit 32. The output terminal of theconnecting circuit 14 is connected to one of input terminals of thedifferential circuit 31. The differential circuit 31differential-amplifies the signal inputted via the connecting circuit14, that is the average output value. The differential-amplified signalis buffered in an output buffer 32 and outputted from the substrateoutput port BN. The output of the substrate output port BN results in avalue in accordance with an average characteristic of the respectiveNMOS transistors QN1, QN2, . . . , QNn in the characteristic monitorcircuit 12 a. In other words, the output of the substrate output port BNresults in an optimum value in accordance with the characteristics ofthe NMOS transistors. A supply substrate voltage outputted from thesubstrate output port BN is outputted to substrates of a plurality ofMOS transistors not shown and also commonly supplied to the substratesof the n number of NMOS transistors QN1, QN2, . . . , QNn in thecharacteristic monitor circuit 12 a.

The n number of NMOS transistors QN1, QN2, . . . , QNn in thecharacteristic monitor circuit 12 a are independently and individuallyevaluated dispersively in the time-shifting manner. However, themonitoring result thereof is averaged when it is reflected on thegeneration of the substrate potential.

As described, when the n number of NMOS transistors QN1, QN2, . . . ,QNn in the characteristic monitor circuit 12 a are dispersively operatedin the time-shifting manner, the NBTI phenomenon generated in the NMOStransistors QN1, QN2, . . . , QNn as a result of the lengthy use isalleviated, and a circuit configuration not easily affected by theage-related deterioration can be realized.

In the foregoing description, one of the NMOS transistor is conductedand evaluated at an optional time point, however, at least two NMOStransistors may be simultaneously conducted and evaluated in therespective periods. Importantly, the substrate potential in accordancewith the operation state of the semiconductor device can besubstantially constantly outputted from the substrate output port BN ofthe substrate potential generating circuit 11 a irrespective of which ofthe NMOS transistors QN1, QN2, . . . , QNn is in the conducted state ina certain period. To put it differently, the n number of NMOStransistors QN1, QN2, . . . , QNn connected in parallel in thecharacteristic monitor circuit 12 a are dispersively operated in thetime-shifting manner so as to avoid any influence on the output of thesubstrate potential generating circuit 11 a.

Further, in the foregoing description, the switch element S3 is turnedon in the sample hold circuit 14 a when the data is held. However, theswitch element S3 may not be necessarily turned on at the time ofholding the data as long as it is turned off when the NMOS transistor isevaluated. Because the average output value of the plurality of samplehold circuits 14 a is inputted to the substrate potential generatingcircuit 11 a, the number of the sample hold circuits 14 a for outputtingthe values is irrelevant as long as the respective sample hold circuits14 a output the values which are correctly evaluated.

Further, in the foregoing description, the timing signal φi (i=1,2, . .. , n) is separately applied to the gates of the respective NMOStransistors to realize the switchover of the n number of NMOStransistors QN1, Qn2, . . . , QNn to and from the conducted state andthe non-conducted state. Alternatively, for example, the switch elementsmay be inserted between the sources of the respective NMOS transistorsand the current supplies, wherein the respective switch elements areindividually controlled so as to switch to and from the conducted stateand the non-conducted state.

The present embodiment described the substrate potential generatingcircuit for generating the substrate potential of the NMOS transistor.However, the ordinarily skilled in the art can easily modify theconstitution according to the present embodiment in such manner that thesubstrate potential generating circuit generates a substrate potentialof a PMOS transistor.

Second Preferred Embodiment

Referring to FIGS. 6 through 8, a semiconductor device according to thesecond preferred embodiment of the present invention is described.

The second preferred embodiment relates to an example of an I/O padcircuit. In the present embodiment, the first semiconductor integratedcircuit 11 is a tristate buffer, and the second semiconductor integratedcircuit 12 is a pull-up circuit.

FIG. 6 shows circuit diagrams illustrating constitutions of a tristatebuffer 11 b and a pull-up circuit 12 b. The tristate buffer 11 b buffersan input signal using an activation signal and outputs the bufferedsignal. The pull-up circuit 12 b serves to prevent a high impedanceoutput from being destabilized when the tristate buffer 11 b isinactivated. The pull-up circuit 12 b comprises three PMOS transistorsQP1, QP2 and QP3. Sources of the PMOS transistors QP1, QP2 and QP3 areconnected to power-supply terminals, while drains thereof are commonlyconnected to an output terminal of the tristate buffer 11 b. Timingsignals φ1, φ2 and φ3 from a pulse generating circuit 13 areindividually applied to gates of the PMOS transistors QP1, QP2 and QP3.

The three PMOS transistors QP1, QP2 and QP3 correspond to theconventional single PMOS transistor in the conducted state.

FIG. 7 is a circuit diagram illustrating a constitution of the pulsegenerating circuit 13. The pulse generating circuit 13 comprises threedelay elements D1, D2 and D3 and constitutes a ring oscillator in whichan output terminal of the delay element D1 is connected to an inputterminal of the delay element D2, an output terminal of the delayelement D2 is connected to an input terminal of the delay element D3,and an output terminal of the delay element D3 is connected to an inputterminal of the delay element D1. The timing signals φ1, φ2 and φ3respectively outputted from the delay elements D1, D2 and D3 are inputsignals to the gates of the PMOS transistors QP1, QP2 and QP3 in thepull-up circuit 12 b.

FIG. 8 shows waveforms of the timing signals φ1, φ2 and φ3 and anaverage voltage value of the timing signals φ1, φ2 and φ3. The waveformsof the timing signals φ1, φ2 and φ3 have an identical frequency anddifferent phases. The average voltage value of the three timing signalsφ1, φ2 and φ3 is constant per unit time. Transition probabilities of thePMOS transistors QP1, QP2 and QP3 whose respective gates input thetiming signals φ1, φ2 and φ3 are equal to one another, and such apull-up resistance that as if a single PMOS transistor were constantlyin the conducted state is realized.

A summed pull-up current capacity of the three PMOS transistors QP1, QP2and QP3 can be substantially equal to a pull-up current capacity of thesingle PMOS transistor constantly conducted. Therefore, the pull-up canbe realized in the same manner as in the conventional technology, whilethe age-related deterioration resulting from the NBTI phenomenon due tothe lengthy use is reduced to approximately ⅓ in comparison to theconventional technology. Accordingly, an extended life can be reliablyassured in the I/O pad circuit in which the pull-up resistance isimportant.

In the foregoing description, the three PMOS transistors are provided,however, the present embodiment is not limited thereto. Further, theNMOS transistor may be used in place of the PMOS transistor. Further,the pulse generating circuit 13 may not necessarily be constituted insuch manner that the plurality of delay elements is connected in thering shape. Importantly, the function obtained in theconstantly-conducted single transistor is realized by dispersivelyoperating the plurality of MOS transistors in the time-shifting manner.In other words, the plurality of MOS transistors is dispersivelyoperated in the time-shifting manner so as to avoid any influence on theoutput of the tristate buffer 11 b.

Further, in the foregoing description, the timing signal φ1 (i=1, 2, 3)is separately applied to the gates of the respective PMOS transistors torealize the switchover of the three PMOS transistors QP1, QP2 and QP3 toand from the conducted state and the non-conducted state. Alternatively,for example, the switch elements may be inserted between the sources ofthe respective PMOS transistors and the current supplies, wherein therespective switch elements are individually controlled so as to switchto and from the conducted state and the non-conducted state.

Third Preferred Embodiment

Referring to FIGS. 1 through 9, a semiconductor device according to thethird preferred embodiment is described.

The third preferred embodiment relates to an example of a dynamiccircuit. In the present embodiment, a dynamic circuit constitutes thefirst semiconductor integrated circuit 11, and a keeper circuitconstitutes the second semiconductor integrated circuit 12.

FIG. 9 shows circuit diagrams illustrating constitutions of a dynamiccircuit 11 c and a keeper circuit 12 c. In the dynamic circuit 11 c, aPMOS transistor QP11 and an NMOS transistor QN 11 activated by a clocksignal and NMOS transistors QN21 and QN22 switched at a high speed inresponse to the application of input signals A and B to gates thereofare serially connected. An output signal C corresponding to the inputsignals A and B is outputted from a drain connecting point of the PMOStransistor QP11 and the NMOS transistor QN21. The keeper circuit 12 c isprovided in order to deal with a floating state of the output in thedynamic circuit 11 c.

The keeper circuit 12 c comprises three PMOS transistors QP21, QP22 andQP23, and three NAND circuits NA11, NA12 and NA13. Sources of the PMOStransistors QP21, QP22 and QP23 are connected to power-supply terminals,while drains thereof are connected to an output of the dynamic circuit11 c. Gates of the PMOS transistors QP21, QP22 and QP23 are connected tooutputs of the corresponding NAND circuits NA11, NA12 and NA13. Oneinputs of the NAND circuits NA11, NA12 and NA13 are connected to theoutput of the dynamic circuit 11 c, while another inputs thereof areconnected to outputs of timing signals φ1, φ2 and φ3 of a pulsegenerating circuit 13. A constitution of the pulse generating circuit 13is the same as in the example of the second preferred embodiment (FIG.7), and not described here again. Waveforms of the timing signals φ1, φ2and φ3 are also the same as in the example of the second preferredembodiment (FIG. 8), and not described here again. The NAND circuitsNA11, NA12 and NA13 serve as inverters.

A summed pull-up current capacity of the three PMOS transistors QP21,QP22 and QP23 can be arranged to be substantially equal to the pull-upcurrent capacity of the single PMOS transistor constantly conducted.Therefore, the pull-up can be realized in the same manner as in theconventional technology, and the age-related deterioration resultingfrom the NBTI phenomenon due to the lengthy use can be reducedapproximately ⅓ in comparison to the conventional technology. As aresult, a reliable long life can be assured in the keeper circuitcorresponding to the dynamic circuit in which the pull-up resistance isimportant.

In the foregoing description, the three PMOS transistors are provided,however, the present embodiment is not limited thereto. Further, theNMOS transistor may be provided in place of the PMOS transistor.Importantly, the same function as in the single transistor constantlyconducted is realized by dispersively operating the plurality of MOStransistors in the time-shifting manner. In other words, the pluralityof MOS transistors can be dispersively operated in the time-shiftingmanner so that the output of the dynamic circuit 11 c is not therebyaffected.

Further, in the foregoing description, the timing signal φi (i=1, 2, 3)is separately applied to the NAND circuits NA11, NA12 and NA13 connectedto the gates of respective PMOS transistors to realize the switchover ofthe three PMOS transistors QP21, QP22 and QP23 to and from the conductedstate and the non-conducted state. Alternatively, for example, theswitch elements may be inserted between the sources of the respectiveNMOS transistors and the current supplies, wherein the respective switchelements are individually controlled so as to switch to and from theconducted state and the non-conducted state.

The present embodiment can be easily applied to a keeper circuit of adomino circuit and the like.

Fourth Preferred Embodiment

Referring to FIGS. 10 through 13, a semiconductor device according to afourth embodiment of the present invention is described.

In the fourth preferred embodiment, instead of inputting the pluralityof gate signals having the equal transition probability to the gates ofthe MOS elements in the time-shifting manner as described in the firstthrough third preferred embodiments, a signal is logically formed usinga CMOS logic circuit, a load of the NBTI applied to one MOS element isdispersed into a plurality of MOS elements.

FIG. 10 shows a two-input NAND circuit. The two-input NAND circuitoutputs an inversion signal of a signal IN as a signal OUT when a signalEN is “H”, while outputting “H” as the signal OUT irrespective of avalue of the signal IN when the signal EN is “L”. The two-input NANDcircuit constituted as described is used, for example, for clock gating.To describe the clock gating, if a clock is supplied or not supplied iscontrolled depending on if a circuit as an gating object is activated ornon-activated. When the object circuit is activated in a short periodand non-activated in a long period in the clock gating, a gate of a PMOStransistor in the two-input NAND circuit is on an ON-voltage side in anextended period and largely affected by the NBTI. In the presentembodiment, the age-related deterioration due to the NBTI in the PMOStransistor in the foregoing case is alleviated. It is needless to saythat the present embodiment is applicable irrespective of the NANDcircuit and clock gating.

FIG. 11 shows a specific circuit diagram of the two-input NAND circuitaccording to the present embodiment, which is logically equivalent tothe NAND circuit shown in FIG. 10. The two-input NAND circuit accordingto the present embodiment comprises a Logic 10E for internallygenerating an EN1 signal and an EN2 signal based on the EN signal and aNAND 10C for inputting the EN1 signal and the EN2 signal generated inaddition to the IN signal and outputting a NAND logic signal of the INsignal and the EN signal. In the Logic 10E, the EN signal is inputted toa clock CLK of a flip-flop 10D, and an inversion output NQ of theflip-flop 10D is inputted to data D of the flip-flop 10D. A switch SW10Bcontrolled by an output Q of the flip-flop 10D communicates the signalEN to the EN2 when the Q is “H”. A switch SW10A controlled by an NQ ofthe flip-flop 10D communicates the signal EN to the EN1 when the NQ is“H”. More specifically, every time when the EN is “H”, a value of theinput signal EN is communicated alternately to the EN1 and EN2.

FIG. 12 shows an example of truth value list of the signals EN, Q, EN1,EN2, IN and OUT. As shown in Fig 0.12, when the signal EN is “L”, thesignal L is communicated to one of the EN1 and EN2. In the NAND 10 c,when one of the EN1 and EN2 is “L”, one of the two PMOS transistorsdisposed in parallel, in which the EN1 and EN2 are inputted to thegates, is conducted, while one of two NMOS transistors seriallydisposed, in which the EN1 and EN2 are inputted to the gates, isnon-conducted. More specifically, the OUT results in “H” irrespective ofthe value of the IN, and the two-input NAND circuit according to thepresent embodiment is logically equivalent to the two-input NAND circuitshown in FIG. 10. Further, as long as the gate of one of the PMOStransistors inputting the EN1 and EN2 to the gates thereof is “L”, theconducted state is obtained. As a result, the deterioration due to theNBTI is dispersed into the two PMOS transistors.

FIG. 13 shows an example in which the two-input NAND circuit accordingto the present embodiment is applied to the clock gating. The two-inputNAND circuit comprising the Logic 10E and the NAND 10C outputs theinversion signal of the clock when the EN signal is “H”, while fixingthe clock to “H” when the EN signal is “L”. In other words, when thecircuit as a destination of the clock supply is non-activated, the EN isfixed to “L”. In the NAND shown in the lower part of the drawing, one ofthe inputs thereof is fixed to “H”, meaning that the inversion signal ofthe clock is constantly supplied to the circuit. The deterioration dueto the NBTI is intensified when the gate of the PMOS transistor is fixedto “L”. According to the constitution of the present embodiment, thedeterioration of the NAND 10C is lessened. As a result, an increase of aclock skew in response to the clock output not subjected to the gatingdue to the age-related deterioration can be reduced.

Fifth Preferred Embodiment

Referring to FIG. 14, a semiconductor device according to a fifthpreferred embodiment of the present invention is described.

FIG. 14 shows a characteristic monitor circuit in which thecharacteristic monitor circuit 12 a of FIG. 2 connected to the substratepotential generating circuit 11 a of FIG. 4 is differently constituted.In FIG. 14, three NMOS transistors supplied with a common substratevoltage and gate voltage are serially connected. The common gate voltageis set to an optional voltage. The substrate voltage equals to thevoltage value from the substrate output port of the substrate potentialgenerating circuit 11 a.

A drain of an NMOS transistor QN11C is connected to a switch elementSW11E, and if the drain is connected to a monitor output of adifferential circuit 31 via a connecting circuit 14 or connected to aground potential is selected in accordance with a control signal φ1. Toput differently, the drain is connected to a monitor output V1 when theφ1 is “H”, while being connected to the ground potential when the φ1 is“L”. A source of an MOS transistor QN11B is connected to a switchelement SW11D, and if the source is connected to the monitor output ofthe differential circuit 31 via the connecting circuit 14 or connectedto the ground potential is selected in accordance with the controlsignal φ1. To put it differently, the source is connected to the groundpotential when the φ1 is “H”, while being connected to the monitoroutput V1 when the φ1 is “L”. Thus, the MOS transistor QN11C and the MOStransistor QN11B are alternately connected to the ground potential andthe monitor output V1 in a switching manner.

As described, when the MOS transistor to be connected to the monitoroutput is switched in response to the φ1, a voltage to be applied to agate-source voltage Vgs of the MOS transistor QN11B is changed, therebyalleviating any influence from the NBTI. In the present embodiment, itis unnecessary to provide the n number of MOS transistors and the nnumber of sample hold circuits. The age-related deterioration can bereduced by providing only the group of MOS transistors seriallyconnected.

Further, when a drain-source voltage Vds of the MOS transistor QN11C isa value approximate to a threshold value when the φ1 is “H”, while beingas approximate as possible to zero when the φ1 is “L”. In general, theage-related deterioration in the MOS transistor is caused by agenerally-called hot carrier effect other than the NBT1 alreadydescribed. The hot carrier effect results from the drain-source voltageVds, and the deterioration is worsened as the Vds is increased. Morespecifically, the deterioration due to the hot carrier effect is reducedbecause the MOS transistor QN11C is changed as a result of controllingwhich of the MOS transistors is connected to the monitor output usingthe φ1.

Sixth Preferred Embodiment

Referring to FIG. 15, a semiconductor device according to a sixthpreferred embodiment of the present invention is described.

FIG. 15 shows a characteristic monitor circuit in which thecharacteristic monitor circuit 12 a of FIG. 2 connected to the substratepotential generating circuit 11 a of FIG. 4 is differently constituted.In the present embodiment, NMOS transistors QN12B and QN12C areconnected in parallel, and NMOS transistors QN12B, QN12C, QN12D andQN12E are serially connected in three stages. Gates of the respectiveMOS transistors are commonly connected and set to an optional voltage.Substrates of the MOS transistors QN12D and QN12E are commonlyconnected, to which the same voltage as the voltage value from thesubstrate output port of the substrate potential generating circuit 11 ais applied.

A drain of the MOS transistor QN12B is connected to a switch elementSW12F, and if the drain is connected to a monitor output of adifferential circuit 31 or opened is selected in accordance with acontrol signal φ1. In other words, the drain is connected to a monitoroutput V1 when the φ1 is “H”, while being opened when the φ1 is “L”. Adrain of the MOS transistor QN12C is connected to a switch elementSW12H, and if the drain is connected to the monitor output of thedifferential circuit 31 or opened is selected in accordance with thecontrol signal φ1. In other words, the drain is connected to the monitoroutput V1 when the φ1 is “L”, while being opened when the φ 1 is “H”.Thus, the MOS transistor QN12C and the MOS transistor QN12B arealternately connected to the ground potential and the monitor output V1in the switching manner.

As described, when the MOS transistor to be connected to the monitoroutput is switched in response to the 01, any influence from the NBTIcan be alleviated. In the present embodiment, it is unnecessary toprovide the n number of MOS transistors and the n number of sample holdcircuits. The age-related deterioration can be reduced by providing onlyone MOS transistor shown in FIG. 15.

A substrate of the MOS transistor QN12B is connected to a switch elementSW12G, and if the substrate is connected to the substrate output port BNof the substrate potential generating circuit 11 a or connected to theground potential is selected in accordance with a control signal/φ1. Inother words, the substrate is connected to the substrate voltage whenthe φ1 is “H”, while being grounded when the φ1 is “L”. A substrate ofthe MOS transistor QN12C is connected to a switch element SW12I, and ifthe substrate is connected to the substrate output port BN of thesubstrate potential generating circuit 11 a or connected to the groundpotential is selected in accordance with the control signal φ1. In otherwords, the substrate is connected to the substrate voltage when the φ1is “L”, while being grounded when the φ1 is “H”.

The influence from the hot carrier effect also results from thesubstrate voltage, and the deterioration is worsened as the substratevoltage is smaller (back bias). More specifically, the deterioration dueto the hot carrier effect is alleviated because the substrate potentialof the MOS transistor QN11C is changed in response to the 01.

While the invention has been described an illustrated in detail, it isto be clearly understood that this is intended be way of illustrationand example only and is not to be taken by way of limitation, the spiritand scope of this invention being limited only be the terms of thefollowing claims.

1. A semiconductor device comprising: a first semiconductor integratedcircuit having a predetermined function, the first semiconductorintegrated circuit outputting a required output signal; and a secondsemiconductor integrated circuit in which a plurality of MOS elementsfor independently switching to and from a conducted state and anon-conducted state in accordance with a plurality of gate signals eachhaving a different timing are provided and the plurality of MOS elementsis connected in parallel to an output or an input of the firstsemiconductor integrated circuit.
 2. A semiconductor device as claimedin claim 1, further comprising a pulse generating circuit for generatingand outputting the plurality of gate signals each having a differenttiming with respect to the plurality of MOS elements in the secondsemiconductor integrated circuit.
 3. A semiconductor device as claimedin claim 1, wherein drains of the plurality of MOS elements in thesecond semiconductor integrated circuit are connected in parallel to theinput of the first semiconductor integrated circuit.
 4. A semiconductordevice as claimed in claim 3, wherein drains of the plurality of MOSelements are connected in parallel to the input of the firstsemiconductor integrated circuit via respective sample hold circuits. 5.A semiconductor device as claimed in claim 3, wherein the output of thefirst semiconductor integrated circuit is connected to respectivesubstrates of the plurality of MOS elements.
 6. A semiconductor deviceas claimed in claim 5, wherein a characteristic monitor circuitconstitutes the second semiconductor integrated circuit.
 7. Asemiconductor device as claimed in claim 1, wherein an I/O pad circuitconstitutes the first semiconductor integrated circuit.
 8. Asemiconductor device as claimed in claim 1, wherein a pull-up circuitconstitutes the second semiconductor integrated circuit.
 9. Asemiconductor device as claimed in claim 8, wherein a tristate bufferconstitutes the first semiconductor integrated circuit.
 10. Asemiconductor device as claimed in claim 1, wherein a keeper circuitconstitutes the second semiconductor integrated circuit.
 11. Asemiconductor device as claimed in claim 10, wherein a dynamic circuitconstitutes the first semiconductor integrated circuit.
 12. Asemiconductor device as claimed in claim 10, wherein the gate signalswith respect to the plurality of MOS elements in the secondsemiconductor integrated circuit are supplied from an NAND circuit whosetwo inputs are an output signal of the first semiconductor integratedcircuit and a timing signal.
 13. A semiconductor device as claimed inclaim 1, wherein the plurality of gate signals has an identicalfrequency and different phases, and a summed voltage thereof issubstantially constant per unit time.
 14. A semiconductor device asclaimed in claim 1, wherein the plurality of gate signals has an equaltransition probability.
 15. A semiconductor device comprising: aplurality of MOS elements; and a logic circuit for generating aplurality of gate signals inputted to gates of the plurality of MOSelements based on an input signal, the semiconductor device outputting arequired output signal, wherein the plurality of MOS elements isequivalent to the output of the required output signal of thesemiconductor device, and a value of the required output signal isdetermined irrespective of values of the other gate signals when any oneof the plurality of gate signals is a first logic value.
 16. Asemiconductor device comprising: a plurality of MOS elements; and aplurality of switch elements, wherein the plurality of MOS elements isserially connected, gates of the plurality of MOS elements are commonlyconnected, substrates of the plurality of MOS elements are commonlyconnected, an end drain and an end source of the plurality of MOSelements are connected to one sides of the respective switch elements,other sides of the respective switch elements are connected to asemiconductor integrated circuit having a predetermined function, andthe connections of the end drain and the end source are switched over inaccordance with a control signal for controlling the switch elements.17. A semiconductor device comprising: a plurality of MOS elements; anda plurality of switch elements, wherein the plurality of MOS elements isconnected in parallel, gates of the plurality of MOS elements arecommonly connected, substrates and sources or drains of the plurality ofMOS elements are connected to one sides of the respective switchelements, other sides of the respective switch elements are connected toa semiconductor integrated circuit having a predetermined function, andthe connections of the substrates and drains or sources are switchedover in accordance with a control signal for controlling the switchelements.